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module ActiveRecord
module Inheritance
extend ActiveSupport::Concern
included do
# Determine whether to store the full constant name including namespace when using STI
class_attribute :store_full_sti_class, instance_writer: false
self.store_full_sti_class = true
end
module ClassMethods
# Determines if one of the attributes passed in is the inheritance column,
# and if the inheritance column is attr accessible, it initializes an
# instance of the given subclass instead of the base class
def new(*args, &block)
if (attrs = args.first).is_a?(Hash)
if subclass = subclass_from_attrs(attrs)
return subclass.new(*args, &block)
end
end
# Delegate to the original .new
super
end
# True if this isn't a concrete subclass needing a STI type condition.
def descends_from_active_record?
if self == Base
false
elsif superclass.abstract_class?
superclass.descends_from_active_record?
else
superclass == Base || !columns_hash.include?(inheritance_column)
end
end
def finder_needs_type_condition? #:nodoc:
# This is like this because benchmarking justifies the strange :false stuff
:true == (@finder_needs_type_condition ||= descends_from_active_record? ? :false : :true)
end
def symbolized_base_class
@symbolized_base_class ||= base_class.to_s.to_sym
end
def symbolized_sti_name
@symbolized_sti_name ||= sti_name.present? ? sti_name.to_sym : symbolized_base_class
end
# Returns the class descending directly from ActiveRecord::Base, or
# an abstract class, if any, in the inheritance hierarchy.
#
# If A extends AR::Base, A.base_class will return A. If B descends from A
# through some arbitrarily deep hierarchy, B.base_class will return A.
#
# If B < A and C < B and if A is an abstract_class then both B.base_class
# and C.base_class would return B as the answer since A is an abstract_class.
def base_class
unless self < Base
raise ActiveRecordError, "#{name} doesn't belong in a hierarchy descending from ActiveRecord"
end
if superclass == Base || superclass.abstract_class?
self
else
superclass.base_class
end
end
# Set this to true if this is an abstract class (see <tt>abstract_class?</tt>).
# If you are using inheritance with ActiveRecord and don't want child classes
# to utilize the implied STI table name of the parent class, this will need to be true.
# For example, given the following:
#
# class SuperClass < ActiveRecord::Base
# self.abstract_class = true
# end
# class Child < SuperClass
# self.table_name = 'the_table_i_really_want'
# end
#
#
# <tt>self.abstract_class = true</tt> is required to make <tt>Child<.find,.create, or any Arel method></tt> use <tt>the_table_i_really_want</tt> instead of a table called <tt>super_classes</tt>
#
attr_accessor :abstract_class
# Returns whether this class is an abstract class or not.
def abstract_class?
defined?(@abstract_class) && @abstract_class == true
end
def sti_name
store_full_sti_class ? name : name.demodulize
end
protected
# Returns the class type of the record using the current module as a prefix. So descendants of
# MyApp::Business::Account would appear as MyApp::Business::AccountSubclass.
def compute_type(type_name)
if type_name.match(/^::/)
# If the type is prefixed with a scope operator then we assume that
# the type_name is an absolute reference.
ActiveSupport::Dependencies.constantize(type_name)
else
# Build a list of candidates to search for
candidates = []
name.scan(/::|$/) { candidates.unshift "#{$`}::#{type_name}" }
candidates << type_name
candidates.each do |candidate|
begin
constant = ActiveSupport::Dependencies.constantize(candidate)
return constant if candidate == constant.to_s
rescue NameError => e
# We don't want to swallow NoMethodError < NameError errors
raise e unless e.instance_of?(NameError)
end
end
raise NameError, "uninitialized constant #{candidates.first}"
end
end
private
# Called by +instantiate+ to decide which class to use for a new
# record instance. For single-table inheritance, we check the record
# for a +type+ column and return the corresponding class.
def discriminate_class_for_record(record)
if using_single_table_inheritance?(record)
find_sti_class(record[inheritance_column])
else
super
end
end
def using_single_table_inheritance?(record)
record[inheritance_column].present? && columns_hash.include?(inheritance_column)
end
def find_sti_class(type_name)
if store_full_sti_class
ActiveSupport::Dependencies.constantize(type_name)
else
compute_type(type_name)
end
rescue NameError
raise SubclassNotFound,
"The single-table inheritance mechanism failed to locate the subclass: '#{type_name}'. " +
"This error is raised because the column '#{inheritance_column}' is reserved for storing the class in case of inheritance. " +
"Please rename this column if you didn't intend it to be used for storing the inheritance class " +
"or overwrite #{name}.inheritance_column to use another column for that information."
end
def type_condition(table = arel_table)
sti_column = table[inheritance_column.to_sym]
sti_names = ([self] + descendants).map { |model| model.sti_name }
sti_column.in(sti_names)
end
# Detect the subclass from the inheritance column of attrs. If the inheritance column value
# is not self or a valid subclass, raises ActiveRecord::SubclassNotFound
# If this is a StrongParameters hash, and access to inheritance_column is not permitted,
# this will ignore the inheritance column and return nil
def subclass_from_attrs(attrs)
subclass_name = attrs.with_indifferent_access[inheritance_column]
return nil if subclass_name.blank? || subclass_name == self.name
unless subclass = subclasses.detect { |sub| sub.name == subclass_name }
raise ActiveRecord::SubclassNotFound.new("Invalid single-table inheritance type: #{subclass_name} is not a subclass of #{name}")
end
subclass
end
end
private
# Sets the attribute used for single table inheritance to this class name if this is not the
# ActiveRecord::Base descendant.
# Considering the hierarchy Reply < Message < ActiveRecord::Base, this makes it possible to
# do Reply.new without having to set <tt>Reply[Reply.inheritance_column] = "Reply"</tt> yourself.
# No such attribute would be set for objects of the Message class in that example.
def ensure_proper_type
klass = self.class
if klass.finder_needs_type_condition?
write_attribute(klass.inheritance_column, klass.sti_name)
end
end
end
end
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